The project seeks to specify input-output relations that characterize how human beings perceive the intensity of odorants and irritants. Subjects will assess perceived intensity by means of various direct psychophysical procedures (e.g., magnitude estimation, intramodality matching). The stimuli will comprise a variety of malodorants and pollutants (e.g., trimethylamine), irritants (e.g., acrolein), and masking-agents. Attention will focus on a) the mathematical relation between the perceived magnitude of a mixture and the perceived magnitude of its unmixed components, b) the ability of one substance to mask another, c) the course of adaptation to a mixture and its components, and d) the relative contributions of the trigeminal and olfactory nerves to perceived odor magnitude and irritation. Both physical and dichorhinic mixtures will be studied in an effort to decide the relative contributions of central and peripheral olfactory structures to phenomena such as masking and adaptation. Key goals are to predict how intense a simple or complex odorous stimulus or irritant will seem to an observer under a variety of conditions (e.g., long-term vs short-term exposure), and to anticipate what effect an air-borne odor modifier (masking-agent, counteractant) will have on perceived odor level. The information gained can be put to use in the development of more reliable means to assess indoor and outdoor odor levels.